1. Field of the Invention
This invention generally relates to an ambient light-regulated power control arrangement for outdoor lighting systems and, more particularly, to a field-adjustable power control arrangement and method of controlling power thereof, as well as to a method of adjusting the timing thereof.
2. Description of the Prior Art
Various power control arrangements have been employed for automatically controlling outdoor lighting systems such as streetlighting loads, highway lighting loads, and area lighting loads. Typical area lighting loads are parking lots, parks, building perimeters, and advertising billboards. The automatic control of such arrangements guards against forgetfulness in operating the lighting system, prevents the isolation of the position of the lighting system from preventing the proper operation thereof, and promotes the efficient and economical utilization of energy.
The power control arrangements in current use for outdoor lighting systems are typically photoelectrically regulated by ambient light conditions, and are operative to automatically turn the lighting system on at dusk, off at dawn and, particularly in the case of area lighting loads, off sometime during the night. An example of an ambient light-regulated power control arrangement is shown in U.S. Pat. No. 3,916,183, which was assigned to the same assignee as the present invention.
Although generally satisfactory for their intended purpose, the known power control arrangements have not proven to be altogether satisfactory in the aspect of resetting the timing when the lighting system is turned off sometime during the night. For example, the power control arrangement described in the above patent employs mechanical timing components including motor-driven memory and timing gear wheels, each having a fixed number of gear teeth, and each having timing contacts spaced in a mutually fixed orientation so as to establish a fixed timing cycle. In the event that one wished to change the timing cycle of such a mechanical arrangement, the entire arrangement must be taken apart, the gear wheels may have to be replaced, and the placement of the timing contacts may have to be changed. This can be done only with great difficulty in the field, if at all. As a practical matter, the timing cycle for any particular application is established in the factory at the time of manufacture, and subsequent adjustment is not feasible.
Another desirable feature not found in power control arrangements in current use is to automatically turn on an area lighting system in the pre-dawn hours. Particularly in the wintertime, when it is still very dark outdoors in the pre-dawn hours, it is desirable to provide additional illumination to assist the flow of traffic and people, particularly children. In order to add this morning turn-on feature to existing installations using mechanical timing arrangements of the type described above, an extensive retrofitting operation is required, thereby effectively preventing this desirable option from being implemented.